One thing that usually comes up in invented fantasy worlds, even if just in passing, is the need to exchange money for good and services.

Rare is the story where you can focus on a strange way to do it – most of the time is it little more than colour. Worlds based on Dungeons and Dragons usually have “gold pieces” as the core value (often abbreviated to “gp”) plus lesser values in silver and copper. Which is kind of ironic because the original idea of “gold piece” was so that game writers could create some local colour by changing the name. Many don’t, of course.

It also ignores some of the economic history of our own world. In medieval Europe, which is the basis for a lot of fantasy fiction world-building, the average man-in-the-field never ever saw gold in his entire life. Gold was rare and thus highly valuable. Too valuable, in fact: silver was much less rare and so many coins were struck in silver. But even a single English silver penny was worth a lot: Wikipedia tells us that estimates of its equivalent value in today’s terms is something like $20. That tells us that a lot of local trade wasn’t transacted with money. No wonder few people ever saw gold.

However, bartering is a lost art today. It isn’t a sin to create a fantasy world with similar mercantile behaviour to our own. It doesn’t usually need to be so different that it throws the reader out of the story. It just has to be different enough.

Terry Pratchett had a very interesting take on money in a Georgian-like Ankh-Morpork in the novel “Making Money”. In it, we finally discover that Ankh-Morpork actually has multiple denominations of coins from fractions of a penny up to several dollars. But strangely no banknotes. One of the plots in this novel is how reformed con-artist Moist von Lipwig, Ankh-Morpork’s postmaster, invents banknotes, having seen his paper postage stamps become a de facto currency. Sir Terry is typically brilliant with this subject matter, especially around the inertia the small business men have for using coins.

Curiously, the world of Harry Potter is also still stuck in a coins-only mode. There seems to be just the three coins, gold Galleons, silver Sickles and copper Knuts. (Rowling also described their relationship as 17 Sickles to a Galleon and 29 Knuts to a Sickle, which sounds like weirdness just for weirdness’ sake. I wonder if she regrets that.) Large sums of money are depicted as sacks of coins, which is nice and old-worlde-like as suits the depiction of the wizardly world. But it’s unwieldy, all the same. This is even implied a few times in the novels.

But because the wizardly world exists alongside our modern world, the few prices we see are generally similar to modern day prices. Not so in Ankh-Morpork. There are subtle references throughout all of Sir Terry’s novels about what an Ankh-Morpork dollar can buy. And compared to today, it’s usually quite a lot.

All money undergoes inflation eventually. This is where the same amount can buy less over time. In today’s modern, interconnected world, you can see inflation happen. But in a medieval fantasy world the economic changes simply happen much slower. This is why a character can pay a penny or two for a mug of ale. You will probably to think about what a penny might really buy in your invented world.

You may also need to consider where your characters get their money from.

This could be a real problem for itinerant adventurers. In the more stereotypical of works, pillaging the treasure vaults of vanquished monsters would be enough. Dungeons and Dragons depends on this to provide the player characters money. It happens in many stories set in their worlds, too. It is tropish, but it solves a problem. The other main alternative is that the demands of hospitality are often different in such a world than today. Food and shelter are much easier to come by when you have the understanding that you would be providing the same to someone else at a different point in life. Or it could be simply the done thing at a certain level of society. This tends to work better with more well-off characters, such as local lords or kings, who can usually afford to do this whether or not they will be repaid.

David Eddings used this latter solution. The kings and rulers of all the countries in the world of The Belgariad are major supporting characters and actually already know most of the main characters. This solved a number of instances of “where do we sleep tonight”. But Eddings also had another creative solution: one of their party was a very canny trader. Prince Kheldar, usually going by the name Silk, was a master at buying low and selling high. He did this several times throughout their adventure in order to replenish Belgarath’s purse.

I wouldn’t put a character like Silk in my writing. Not in the foreground, at least. He is an elegant solution to a problem, but I feel he has become a bit of a trope himself. I am more inclined to give my characters something approaching a “real” job or some sort. It tends to mean they have to work or fight for their living, but there are stories in that.

Every society has a way to measure the worth of exchanged goods. You don’t have to go all out on how your world’s economics works, but you should be aware that it needs to. At the very least, you need to know how it applies to your character.